Have a friend who can't get his machine to update at all. it will download and start installing and then almost instantly fail with ""windowsUpdate_800B0100" " WindowsUpdate_dt000"

All the search results I found for that error seem to be about having trouble installing SP1, but this machine is already running SP1 (and has all updates installed except the one thats failing, KB2778344).

I tried quite a few things, renaming the software distribution folder so it would download it fresh (this helped a little but, there was initially 3 updates failing and this let me install two of them), running the fixit to reset/repair windows update, running the system update readiness tool, using the windows update troubleshooter in control panel. I also scanned for malware with malwarebytes which found 2 items in the user's internet explorer temp files and removed them, didn't find anything else and shows no other symptoms of malware.

Recently had a problem with Win 8 laptop erroring out for WU, to fix I had to:

Stop the Windows Update service in services.msc

then delete the contents of:

SoftwareDistribution\DataStore

and

SoftwareDistribution\Download

Then restart Windows update service and check for updates again

All worked fine after that

Yeah I did try that (just different method, renamed entire SoftwareDistrobution folder to Softwaredistrobution.old, and let windows regenerate the folder). This helped for 2/3 updates that were failing, but one continues to. I even tried doing it again and rebooting but it didn't help.

whew, think I've got it now. ended up having to download the .msu package for the update that checksur was complaing was corrupted (KB2761226), extracting the files from it, placing them in the correct directories under C:\Windows\Temp\CheckSUR, run the windows update readiness checker again, and now it was able to fix most of the problems. Its still complaining about a few files but I think I just missed a few files to manually copy over, so I just have to try again, it fixed most of the errors

whew, think I've got it now. ended up having to download the .msu package for the update that checksur was complaing was corrupted (KB2761226), extracting the files from it, placing them in the correct directories under C:\Windows\Temp\CheckSUR, run the windows update readiness checker again, and now it was able to fix most of the problems. Its still complaining about a few files but I think I just missed a few files to manually copy over, so I just have to try again, it fixed most of the errors

Maybe try an sfc /scannow and see if anything gets repaired / replaced

Yeah if it still doesn't work I will, right now I've copies over the files I think I missed and am running checksur again, and its already repaired a few more things, so hopefully this is the last of the corrupted files: